Since the major nuclear accidents, one of the main focus in the safety nuclear field has been on passive safety systems. These systems perform the same functions as active systems, but without the use of energy or human intervention. The SESI/LEMS laboratory, in the field of research, analysis and modelling of passive systems, proposes a new configuration for the Automatic Depressurisation System (ADS) already present in the AP1000 reactor. In particular, the new configuration involves the addition of a tank called LPWT (Low Pressure Water Tank) into which is injected the steam produced in the primary circuit in the event of an Loss of Coolant accident.